Tissue repair plays an important role in the biological response to nephrotoxic damage by environmental chemicals which are activated to reactive chemical species. The kidney is a major target for chemical toxins due to its role in xenobiotic metabolism. Though the mechanisms of nephrotoxin activation and cellular toxicity are becoming more clear, the mechanism for repair of chemical damage are poorly understood. We do know, that the proximal tubule epithelial cells repair damage by replacing dead cells through, proliferation of remaining cells, however, we do not know what controls the proliferative response. Since repairing the tissue damage may be of equal importance to the activation step in the overall response of the kidney to environmental toxins, it is important to understand the repair process. With this knowledge, our future goal will be to assess the effect of continued exposure to environmental pollutants on the repair process itself. This is critical since environmental exposure tend to be chronic rather than acute, and the ability to inhibit repair may contribute to organ damage. Our goal is to elucidate the mechanisms of tissue repair in the kidney (nephrogenic repair). We propose that regulators, Including growth factors and extracellular matrix, control the phases of the repair process: 1) entry into the cell cycle, 2) growth of cells, 3) cessation of growth, and 4) differentiation. Markers for each phase in vivo have been established as has a method for culturing rat kidney proximal tubule epithelial' cells which express the same markers for growth and differentiation appropriately. Therefore, a combination of in vivo and in vitro approaches will be used to facilitate the investigations and to cross-check and verify results. Changes in growth factor expression associated with each phase of nephrogenic repair (as identified by markers) will be determined in vivo using cDNA probes and/or antibodies. Once these factors have been identified, the mechanisms through which they control cell growth and differentiation can be elucidated in vitro using the tissue culture model. Protein kinases play a major role as regulators of growth factor action, therefore,, the role of protein kinases in nephrogenic repair will be determined. Specifically, substrates for growth factor-regulated protein kinases will be identified in kidney epithelial cells. Finally, the role of extracellular matrix in controlling the ability of kidney cells to differentiate will be evaluated by determining the expression of differentiation markers by the cultured renal epithelial cells.